O3 Layer Research Articles

Low temperature plasma‐enhanced ALD TiN ultrathin films for Hf0.5Zr0.5O2‐based ferroelectric MIM structures

In this work chemical and electrical properties of TiN films, grown by low temperature plasma‐enhanced atomic layer deposition (PE‐ALD) process from TiCl4 and NH3, were investigated. Electrical resistivity as low as 250 μOhm × cm, as well as the lowest Cl impurity content, was achieved at 320 °C. Full‐ALD Hf0.5Zr0.5O2‐based metal‐ferroelectric‐metal capacitor with TiN electrodes was fabricated and its electrical properties were investigated. It was also shown that the proposed PE‐ALD process provides an early film continuity, which was confirmed by ultrathin fully continuous film growth. Such ultrathin (3 nm) and fully continuous TiN film was also successfully implemented as the top electrode to Hf0.5Zr0.5O2‐based ferroelectric capacitor. Angle‐resolved X‐ray photoelectron spectroscopy (AR‐XPS) was used for its thickness determination and a visible wake‐up effect in underlying Hf0.5Zr0.5O2 layer was clearly observed.

Superior Stable and Long Life Sodium Metal Anodes Achieved by Atomic Layer Deposition.

Na-metal batteries are considered as the promising alternative candidate for Li-ion battery beneficial from the wide availability and low cost of sodium, high theoretical specific capacity, and high energy density based on the plating/stripping processes and lowest electrochemical potential. For Na-metal batteries, the crucial problem on metallic Na is one of the biggest challenges. Mossy or dendritic growth of Na occurs in the repetitive Na stripping/plating process with an unstable solid electrolyte interphase layer of nonuniform ionic flux, which can not only lead to the low Coulombic efficiency, but also can create short circuit risks, resulting in possible burning or explosion. In this communication, the atomic layer deposition of Al2 O3 coating is first demonstrated for the protection of metallic Na anode for Na-metal batteries. By protecting Na foil with ultrathin Al2 O3 layer, the dendrites and mossy Na formation have been effectively suppressed and lifetime has been significantly improved. Furthermore, the thickness of protective layer has been further optimized with 25 cycles of Al2 O3 layer presenting the best performance over 500 cycles. The novel design of atomic layer deposition protected metal Na anode may bring in new opportunities to the realization of the next-generation high energy-density Na metal batteries.

Mechanism of concentration quenching in epitaxial (Er_xSc_1-x)_2O_3 thin layers

We have optically investigated the characteristics of concentration quenching in epitaxial (ErxSc1-x)2O3 layers at the liquid helium temperature as a function of the Er composition (x = 1.000-0.012). Concentration quenching with increasing Er composition was observed at the lowest optical transition energy, although emission lifetimes of 2 ms were maintained from x = 0.012 to 0.270. An analysis of the excitation power dependence of the emission intensity at the lowest and up-converted transition energies revealed that the concentration quenching in high-quality epitaxial (ErxSc1-x)2O3 films mainly originates from the population escaping to the up-conversion states with a high transfer rate, not the population transfer among Er3+ sites to non-radiative centers.

Tunneling electroresistance effect in a Pt/Hf0.5Zr0.5O2/Pt structure

The present work reports the fabrication of a ferroelectric tunnel junction based on a CMOS compatible 2.8 nm-thick Hf0.5Zr0.5O2 tunnel barrier. It presents a comprehensive study of the electronic properties of the Pt/Hf0.5Zr0.5O2/Pt system by X-ray photoelectron and UV-Visible spectroscopies. Furthermore, two different scanning probe techniques (Piezoresponse Force Microscopy and conductive-AFM) were used to demonstrate the ferroelectric behavior of the ultrathin Hf0.5Zr0.5O2 layer as well as the typical current-voltage characteristic of a ferroelectric tunnel junction device. Finally, a direct tunneling model across symmetric barriers was used to correlate electronic and electric transport properties of the ferroelectric tunnel junction system, demonstrating a large tunnel electroresistance effect with a tunneling electroresistance effect ratio of 20.

Self‐Propelled Soft Protein Microtubes with a Pt Nanoparticle Interior Surface

Human serum albumin (HSA) microtubes with an interior surface composed of Pt nanoparticles (PtNPs) are self-propelled in aqueous H2 O2 medium. They can capture cyanine dye and Escherichia coli (E. coli) efficiently. Microtubes were prepared by wet templating synthesis by using a track-etched polycarbonate (PC) membrane with alternate filtrations of aqueous HSA, poly-l-arginine (PLA), and citrate-PtNPs. Subsequent dissolution of the PC template yielded uniform hollow cylinders made of (PLA/HSA)8 PLA/PtNP stacking layers (1.16±0.02 μm outer diameter, ca. 23 μm length). In aqueous H2 O2 media, the soft protein microtubes are self-propelled by jetting O2 bubbles from the open-end terminus. The effects of H2 O2 and surfactant concentrations on the velocity were investigated. The swimming microtube captured cyanine dye in the HSA component of the wall. Addition of an intermediate γ-Fe3 O4 layer allowed manipulation of the direction of movement of the tubule by using a magnetic field. Because the exterior surface is positively charged, the bubble-propelled microtubes adsorbed E. coli with high efficiency. The removal ratio of E. coli by a single treatment reached 99 %.

Tropospheric ozonesonde profiles at long-term U.S. monitoring sites: 2. Links between Trinidad Head, CA, profile clusters and inland surface ozone measurements.

Much attention has been focused on the transport of ozone (O3) to the Western U.S., particularly given the latest revision of the National Ambient Air Quality Standard (NAAQS) to 70 parts per billion by volume (ppbv) of O3. This makes defining a "background" O3 amount essential so that the effects of stratosphere-to-troposphere exchange and pollution transport to this region can be quantified. To evaluate free-tropospheric and surface O3 in the Western U.S., we use self-organizing maps to cluster 18 years of ozonesonde profiles (940 samples) from Trinidad Head, CA. Two of nine O3 mixing ratio profile clusters exhibit thin laminae of high O3 above Trinidad Head. A third, consisting of background (~20 - 40 ppbv) O3, occurs in ~10% of profiles. The high O3 layers are located between 1 and 4 km amsl, and reside above a subsidence inversion associated with a northern location of the semi-permanent Pacific subtropical high. Several ancillary data sets are examined to identify the high O3 sources (reanalyses, trajectories, remotely-sensed carbon monoxide), but distinguishing chemical and stratospheric influences of the elevated O3 is difficult. There is marked and long-lasting impact of the elevated tropospheric O3 on high-altitude surface O3 monitors at Lassen Volcanic and Yosemite National Parks, and Truckee, CA. Days corresponding to the high O3 clusters exhibit hourly surface O3 anomalies of +5 - 10 ppbv compared to a climatology; the anomalies can last up to four days. The profile and surface O3 links demonstrate the importance of regular ozonesonde profiling at Trinidad Head.

Crystal Structure, Defects, Magnetic and Dielectric Properties of the Layered Bi3n+1Ti7Fe3n-3O9n+11 Perovskite-Anatase Intergrowths.

The Bi3n+1Ti7Fe3n-3O9n+11 materials are built of (001)p plane-parallel perovskite blocks with a thickness of n (Ti,Fe)O6 octahedra, separated by periodic translational interfaces. The interfaces are based on anatase-like chains of edge-sharing (Ti,Fe)O6 octahedra. Together with the octahedra of the perovskite blocks, they create S-shaped tunnels stabilized by lone pair Bi3+ cations. In this work, the structure of the n = 4-6 Bi3n+1Ti7Fe3n-3O9n+11 homologues is analyzed in detail using advanced transmission electron microscopy, powder X-ray diffraction, and Mössbauer spectroscopy. The connectivity of the anatase-like chains to the perovskite blocks results in a 3ap periodicity along the interfaces, so that they can be located either on top of each other or with shifts of ±ap along [100]p. The ordered arrangement of the interfaces gives rise to orthorhombic Immm and monoclinic A2/m polymorphs with the unit cell parameters a = 3ap, b = bp, c = 2(n + 1)cp and a = 3ap, b = bp, c = 2(n + 1)cp - ap, respectively. While the n = 3 compound is orthorhombic, the monoclinic modification is more favorable in higher homologues. The Bi3n+1Ti7Fe3n-3O9n+11 structures demonstrate intricate patterns of atomic displacements in the perovskite blocks, which are supported by the stereochemical activity of the Bi3+ cations. These patterns are coupled to the cationic coordination of the oxygen atoms in the (Ti,Fe)O2 layers at the border of the perovskite blocks. The coupling is strong in the n = 3, 4 homologues, but gradually reduces with the increasing thickness of the perovskite blocks, so that, in the n = 6 compound, the dominant mode of atomic displacements is aligned along the interface planes. The displacements in the adjacent perovskite blocks tend to order antiparallel, resulting in an overall antipolar structure. The Bi3n+1Ti7Fe3n-3O9n+11 materials demonstrate an unusual diversity of structure defects. The n = 4-6 homologues are robust antiferromagnets below TN = 135, 220, and 295 K, respectively. They show a high dielectric constant that weakly increases with temperature and is relatively insensitive to the Ti/Fe ratio.

A detailed pathway analysis of the chemical reaction system generating the Martian vertical ozone profile

Atmospheric chemical composition is crucial in determining a planet’s atmospheric structure, stability, and evolution. Attaining a quantitative understanding of the essential chemical mechanisms governing atmospheric composition is nontrivial due to complex interactions between chemical species. Trace species, for example, can participate in catalytic cycles – affecting the abundance of major and other trace gas species. Specifically, for Mars, such cycles dictate the abundance of its primary atmospheric constituent, carbon dioxide (CO2), but also for one of its trace gases, ozone (O3). The identification of chemical pathways/cycles by hand is extremely demanding; hence, the application of numerical methods, such as the Pathway Analysis Program (PAP), is crucial to analyze and quantitatively exemplify chemical reaction networks. Here, we carry out the first automated quantitative chemical pathway analysis of Mars’ atmosphere with respect to O3. PAP was applied to JPL/Caltech’s 1-D updated photochemical Mars model’s output data. We determine all significant chemical pathways and their contribution to O3 production and consumption (up to 80 km) in order to investigate the mechanisms causing the characteristic shape of the O3 volume mixing ratio profile, i.e. a ground layer maximum and an ozone layer at ∼50 km. These pathways explain why an O3 layer is present, why it is located at that particular altitude and what the different processes forming the near-surface and middle atmosphere O3 maxima are. Furthermore, we show that the Martian atmosphere can be divided into two chemically distinct regions according to the O(3P):O3 ratio. In the lower region (below approximately 24 km altitude) O3 is the most abundant Ox (= O3 + O(3P)) species. In the upper region (above approximately 24 km altitude), where the O3 layer is located, O(3P) is the most abundant Ox species. Earlier results concerning the formation of O3 on Mars can now be explained with the help of chemical pathways leading to a better understanding of the vertical O3 profile.

Nanoscale self-templating for oxide epitaxy with large symmetry mismatch

Direct observations using scanning transmission electron microscopy unveil an intriguing interfacial bi-layer that enables epitaxial growth of a strain-free, monoclinic, bronze-phase VO2(B) thin film on a perovskite SrTiO3 (STO) substrate. We observe an ultrathin (2–3 unit cells) interlayer best described as highly strained VO2(B) nanodomains combined with an extra (Ti,V)O2 layer on the TiO2 terminated STO (001) surface. By forming a fully coherent interface with the STO substrate and a semi-coherent interface with the strain-free epitaxial VO2(B) film above, the interfacial bi-layer enables the epitaxial connection of the two materials despite their large symmetry and lattice mismatch.

Photoelectrochemical Performance Observed in Mn-Doped BiFeO₃ Heterostructured Thin Films.

Pure BiFeO3 and heterostructured BiFeO3/BiFe0.95Mn0.05O3 (5% Mn-doped BiFeO3) thin films have been prepared by a chemical deposition method. The band structures and photosensitive properties of these films have been investigated elaborately. Pure BiFeO3 films showed stable and strong response to photo illumination (open circuit potential kept −0.18 V, short circuit photocurrent density was −0.023 mA·cm−2). By Mn doping, the energy band positions shifted, resulting in a smaller band gap of BiFe0.95Mn0.05O3 layer and an internal field being built in the BiFeO3/BiFe0.95Mn0.05O3 interface. BiFeO3/BiFe0.95Mn0.05O3 and BiFe0.95Mn0.05O3 thin films demonstrated poor photo activity compared with pure BiFeO3 films, which can be explained by the fact that Mn doping brought in a large amount of defects in the BiFe0.95Mn0.05O3 layers, causing higher carrier combination and correspondingly suppressing the photo response, and this negative influence was more considerable than the positive effects provided by the band modulation.

Fully ALD-grown TiN/Hf0.5Zr0.5O2/TiN stacks: Ferroelectric and structural properties

Since the discovery of ferroelectricity (FE) in HfO2-based thin films, they are gaining increasing attention as a viable alternative to conventional FE in the next generation of non-volatile memory devices. In order to further increase the density of elements in the integrated circuits, it is essential to adopt a three-dimensional design. Since atomic layer deposition (ALD) processes are extremely conformal, ALD is the favored approach in the production of 3D ferroelectric random access memory. Here, we report the fabrication of fully ALD-grown capacitors comprising a 10-nm-thick FE Hf0.5Zr0.5O2 layer sandwiched between TiN electrodes, which are subjected to a detailed investigation of the structural and functional properties. The robust FE properties of Hf0.5Zr0.5O2 films in capacitors are established by several alternative techniques. We demonstrate a good scalability of TiN/Hf0.5Zr0.5O2/TiN FE capacitors down to 100-nm size and the polarization retention in the test “one transistor-one capacitor” (1T-1C) cells after 1010 writing cycles. The presence of a non-centrosymmetric orthorhombic phase responsible for FE properties in the alloyed polycrystalline Hf0.5Zr0.5O2 films is established by transmission electron microscopy. Given the ability of the ALD technique to grow highly conformal films and multilayered structures, the obtained results indicate the route for the design of FE non-volatile memory devices in 3D integrated circuits.

Ferroelectric triggering of carbon monoxide adsorption on lead zirco-titanate (001) surfaces.

Atomically clean lead zirco-titanate PbZr0.2Ti0.8O3 (001) layers exhibit a polarization oriented inwards P(−), visible by a band bending of all core levels towards lower binding energies, whereas as introduced layers exhibit P(+) polarization under air or in ultrahigh vacuum. The magnitude of the inwards polarization decreases when the temperature is increased at 700 K. CO adsorption on P(−) polarized surfaces saturates at about one quarter of a monolayer of carbon, and occurs in both molecular (oxidized) and dissociated (reduced) states of carbon, with a large majority of reduced state. The sticking of CO on the surface in ultrahigh vacuum is found to be directly related to the P(−) polarization state of the surface. A simple electrostatic mechanism is proposed to explain these dissociation processes and the sticking of carbon on P(−) polarized areas. Carbon desorbs also when the surface is irradiated with soft X-rays. Carbon desorption when the polarization is lost proceeds most probably in form of CO2. Upon carbon desorption cycles, the ferroelectric surface is depleted in oxygen and at some point reverses its polarization, owing to electrons provided by oxygen vacancies which are able to screen the depolarization field produced by positive fixed charges at the surface.

The effect of LaNiO3 thickness on the magnetoelectric response of Pb(Zr0.52Ti0.48)O3 film-on-CoFe2O4 ceramic composites

A magnetoelectric composite of Pb(Zr0.52Ti0.48)O3 film-on-CoFe2O4 ceramic was prepared by spin-coating Pb(Zr0.52Ti0.48)O3 films of 300 nm in thickness on the LaNiO3-buffered highly dense CoFe2O4 ceramics. The X-ray diffraction, ferroelectric loops, piezoelectric curves, and magnetoelectric coupling effects were all measured at room temperature to investigate the effect of LaNiO3 thickness on the magnetoelectric response of the composites. The introduction of the metallic oxide LaNiO3 efficiently enhanced the magnetoelectric coefficient α E by improving the electric-related outputs. However, too thick LaNiO3 layer would also hinder the strain (stress) transferring across the interface between the Pb(Zr0.52Ti0.48)O3 and CoFe2O4 phases. A peak α E value was obtained in the sample with a LaNiO3 thickness of about 60 nm, which was 2.5 times larger than that in the composite of Pb(Zr0.52Ti0.48)O3 film on the CoFe2O4 ceramic without the LaNiO3 layer. Further enhancement could be anticipated by optimizing the LaNiO3 layer and/or Pb(Zr0.52Ti0.48)O3 films.

Ferroelectric, ferromagnetic, magnetodielectric and in-plane ME coupling properties of Pb(Zr0.52Ti0.48)O3–Bi0.9Nd0.1FeO3 bilayer nano-films prepared via Sol–gel processing

Biphasic magnetoelectric composite films composed of Pb(Zr0.52Ti0.48)O3 and Bi0.9Nd0.1FeO3 were successfully fabricated on Pt(111)/Ti/SiO2/Si(100) substrates via Sol–gel and Rapid Thermal Process, forming Pb(Zr0.52Ti0.48)O3/Bi0.9Nd0.1FeO3 and Bi0.9Nd0.1FeO3/Pb(Zr0.52Ti0.48)O3 bilayer structures due to the different deposition sequences. Phase formation and lattice parameters of the tetragonal PZT and rhombohedral BNF were confirmed in X-ray diffractograms. The scan electron micrographs showed that Pb(Zr0.52Ti0.48)O3 layer owns larger and closer grains than the corresponding Bi0.9Nd0.1FeO3 layer. Physical properties testing indicated that such bilayer nanostructures show simultaneously excellent ferroelectric and ferromagnetic properties, as well as conspicuous magnetodielectric and magnetoelectric effects. And meanwhile, the Bi0.9Nd0.1FeO3/Pb(Zr0.52Ti0.48)O3 thin films exhibit better ferroelectric, ferromagnetic, magnetodielectric and in-plane magnetoelectric coupling properties than Pb(Zr0.52Ti0.48)O3/Bi0.9Nd0.1FeO3 films, revealing the influence of interfacial effect caused by deposition sequences of the constituent phases.

Water Oxidation by Size-Selected Co27 Clusters Supported on Fe2 O3.

The complexity of the water oxidation reaction makes understanding the role of individual catalytic sites critical to improving the process. Here, size-selected 27-atom cobalt clusters (Co27 ) deposited on hematite (Fe2 O3 ) anodes were tested for water oxidation activity. The uniformity of these anodes allows measurement of the activity of catalytic sites of well-defined nuclearity and known density. Grazing incidence X-ray absorption near-edge spectroscopy (GIXANES) characterization of the anodes before and after electrochemical cycling demonstrates that these Co27 clusters are stable to dissolution even in the harsh water oxidation electrochemical environment. They are also stable under illumination at the equivalent of 0.4 suns irradiation. The clusters show turnover rates for water oxidation that are comparable or higher than those reported for Pd- and Co-based materials or for hematite. The support for the Co27 clusters is Fe2 O3 grown by atomic layer deposition on a Si chip. We have chosen to deposit a Fe2 O3 layer that is only a few unit cells thick (2 nm), to remove complications related to exciton diffusion. We find that the electrocatalytic and the photoelectrocatalytic activity of the Co27 /Fe2 O3 material is significantly improved when the samples are annealed (with the clusters already deposited). Given that the support is thin and that the cluster deposition density is equivalent to approximately 5 % of an atomic monolayer, we suggest that annealing may significantly improve the exciton diffusion from the support to the catalytic moiety.

Factors Affecting the Performance of Champion Silyl-Anchor Carbazole Dye Revealed in the Femtosecond to Second Studies of Complete ADEKA-1 Sensitized Solar Cells.

Record laboratory efficiencies of dye-sensitized solar cells have been recently reported using an alkoxysilyl-anchor dye, ADEKA-1 (over 14 %). In this work we use time-resolved techniques to study the impact of key preparation factors (dye synthesis route, addition of co-adsorbent, use of cobalt-based electrolytes of different redox potential, creation of insulating Al2 O3 layers and molecule capping passivation of the electrode) on the partial charge separation efficiencies in ADEKA-1 solar cells. We have observed that unwanted fast recombination of electrons from titania to the dye, probably associated with the orientation of the dyes on the titania surface, plays a crucial role in the performance of the cells. This recombination, taking place on the sub-ns and ns time scales, is suppressed in the optimized dye synthesis methods and upon addition of the co-adsorbent. Capping treatment significantly reduces the charge recombination between titania and electrolyte, improving the electron lifetime from tens of ms to hundreds of ms, or even to single seconds. Similar increase in electron lifetime is observed for homogenous Al2 O3 over-layers on titania nanoparticles, however, in this case the total solar cells photocurrent is decreased due to smaller electron injection yield from the dye. Our studies should be important for a broader use of very promising silyl-anchor dyes and the further optimization and development of dye-sensitized solar cells.

Fabrication of α-Ga2O3 Thin Films Using α-(Al x Ga1-x )2O3 Multi Buffer Layers and Its Crysatal Structure Properties

These days, huge attention has been given to power devices using wide bandgap semiconductors, which can lead to energy-saving. We have taken interest in corundum-structured Ga2O3 (α-Ga2O3) having wider bandgap compared with those of SiC and GaN, because it is considered to have much higher endurance voltage and lower on-resistance [1]. By using mist CVD [2], which is a safe, cost-effective, and environmental-friendly growth technology, Sn-doped α-Ga2O3 thin films grown on sapphire substrates showed n-type conductivity with Hall mobility of ~20 cm2/Vs and carrier concentration of about 1019 cm-3,but the mobility markedly decreases when the carrier concentration was controlled at the range of 1017 cm-3 [3]. Because of the large lattice mismatch between α-Ga2O3 and sapphire (4.8 and 3.5% for a- and c-axes), α-Ga2O3 thin films grown on sapphire substrates contain a high dislocation density. Especially edge dislocation density was measured as 7×1010 cm-2 [4], which seems to deteriorate carrier conduction in the α-Ga2O3 layer. It is considered that dislocations trap free electrons and are negatively charged, diminishing the electron mobility due to electron scattering. Aiming at decreasing the dislocation density in α-Ga2O3 thin films and improving the electrical properties, in this study we report the fabrication of the α-Ga2O3 using α-(Al x Ga1-x )2O3 multilayers as a buffer layer overcoming the lattice mismatch between α-Ga2O3and sapphire. The α-Ga2O3 main layer and the α-(Al x Ga1-x )2O3 buffer layers were grown on c-plane sapphire substrate by the mist CVD method. Prior to the growth, a sapphire substrate was annealed in air at 1050oC for 12 hours to form atomically flat and clean surface. The buffer layer consists with 12 pairs of 20-nm thick α-(Al0.9Ga0.1)2O3/α-(Al0.2Ga0.8)2O3 multilayer structure. The thickness ratios for α-(Al0.9Ga0.1)2O3/α-(Al0.2Ga0.8)2O3 were gradually changed from 1 (on sapphire) to 0.09 (top of the buffer layer) so that the average composition of the buffer layer changed from Al-rich (close to sapphire) to Ga-rich (close to Ga2O3). Then, a 150-nm thick α-(Al0.2Ga0.8)2O3 layer was grown on the 12 pairs of α-(Al0.9Ga0.1)2O3/α-(Al0.2Ga0.8)2O3 layers, followed by the growth of a 150-nm thick α-Ga2O3 main layer. The growth of α-Ga2O3 and α-(Al x Ga1-x )2O3 layers were carried out at 470 and 700oC, respectively. From the reciprocal space map for (11-29) reflection, we attributed the three intense reflection patterns originating from the sapphire substrate, the thick α-(Al0.2Ga0.8)2O3 layer on the buffer layer (below the α-Ga2O3 main layer), and the α-Ga2O3 main layer. The α-Ga2O3 and α-(Al0.2Ga0.8)2O3 layers are lattice-relaxed with respect to the sapphire substrate and the α-Ga2O3layer seems to be subject to slight in-plane compressive strain. The cross-sectional transmission electron microscope (TEM) image of the sample observed along the <11-20> zone axis shows that the sample structure consisting with periodic multilayers of α-(Al0.9Ga0.1)2O3 and α-(Al0.2Ga0.8)2O3 is actually fabricated. The thickness of a unit pair of α-(Al0.9Ga0.1)2O3/α-(Al0.2Ga0.8)2O3 was recognized as about 20 nm, which was nearly the same as designed. Cross-sectional TEM images under two-beam conditions were obtained to discuss the dislocation structure of the buffer layers and the α-Ga2O3 main layer. These images reveal that most of the strains are concentrated in the α-(AlxGa1-x)2O3 buffer layers. The densities of screw and edge dislocations in the α-Ga2O3 thin film were approximated as 3×108 and 6×108 cm-2, respectively. By introducing the buffer layers, the edge dislocations in the α-Ga2O3 thin films was successfully reduced from 7×1010 cm-2 (in a α-Ga2O3 thin film directly grown on a sapphire substrate) to 6×108 cm-2 by more than two order of magnitude. By optimizing the structure and growth conditions of the buffer layers, the further improvements in quality of the α-Ga2O3main layer is expected, leading to attractive device performance using inexpensive and large-area sapphire substrates.

Enhanced Electrochemical Performance of Porous Electrodes for All-Solid-State Li-Ion Microbatteries

Nowadays, lithium-ion batteries (LIBs) are widely used to power portable devices, microelectronics, vehicles, etc. With many advantages such as high surface area and improved charge transport, self-supported 3-D nanostructured metal oxides are promising electrode materials for LIBs and their impact is particularly significant when considering the miniaturization of energy storage systems and the development of 3D microbatteries [1-3]. During this talk, it will be presented the fabrication and use of porous electrodes based on titania nanotubes (TiO2nts) as anode [4–8] and LiNi0.5Mn1.5O4 (LNMO) as cathode. This kind of 3D nanostructured electrodes is particularly interesting due to better electrochemical performance in terms of kinetics and stability during cycling. Then, the fabrication of an all-solid-state Rocking-chair battery composed of vertical arrays of TiO2nts as anode, a polymer thin film as electrolyte, and a LiNi0.5Mn1.5O4 (LNMO) layer as cathode will be shown [9]. According to the electrochemical tests, this 2D full-solid microbattery exhibits high performance such as good discharge capacity and good capacity retention. Finally, the current approaches developed to achieve the fabrication of a full 3D microcell will be highlighted. Particularly, the conformal electrodeposition of polymer electrolytes onto the electrodes will be discussed [10-12].

Evaluating Summer-Time Ozone Enhancement Events in the Southeast United States

This study evaluates source attribution of ozone (O3) in the southeast United States (US) within O3 lamina observed by the University of Alabama in Huntsville (UAH) Tropospheric Ozone Lidar Network (TOLNet) system during June 2013. This research applies surface-level and airborne in situ data and chemical transport model simulations (GEOS-Chem) in order to quantify the impact of North American anthropogenic emissions, wildfires, lightning NOx, and long-range/stratospheric transport on the observed O3 lamina. During the summer of 2013, two anomalous O3 layers were observed: (1) a nocturnal near-surface enhancement and (2) a late evening elevated (3–6 km above ground level) O3 lamina. A “brute force” zeroing method was applied to quantify the impact of individual emission sources and transport pathways on the vertical distribution of O3 during the two observed lamina. Results show that the nocturnal O3 enhancement on 12 June 2013 below 3 km was primarily due to wildfire emissions and the fact that daily maximum anthropogenic emission contributions occurred during these night-time hours. During the second case study it was predicted that above average contributions from long-range/stratospheric transport was largely contributing to the O3 lamina observed between 3 and 6 km on 29 June 2013. Other models, remote-sensing observations, and ground-based/airborne in situ data agree with the source attribution predicted by GEOS-Chem simulations. Overall, this study demonstrates the dynamic atmospheric chemistry occurring in the southeast US and displays the various emission sources and transport processes impacting O3 enhancements at different vertical levels of the troposphere.

Silica Wastes to High-Performance Lithium Storage Materials: A Rational Designed Al2 O3 Coating Assisted Magnesiothermic Process

Si/C yolk-shell structures have been developed to deal with the major issues associated with Si anodes: the huge volume changes and the low electrical conductivity. However, the fabrication process often involves expensive starting materials and/or simultaneously generates insulated SiC, which is harmful for Si anodes. Here, silica wastes from the optical fibers industry are used as starting materials to prepare high performance Si/C materials with Si@void@C yolk-shell structure via a rational designed Al2 O3 coating assisted magnesiothermic process. The obtained yolk-shell Si@void@C materials have a capacity of more than 1450 mA h g-1 after 100 cycles at 0.4 A g-1 . Thanks to the easily coated and removed Al2 O3 layer, the general formation of SiC can be avoided which is beneficial for improving the rate performances, and a capacity of ≈800 mA h g-1 is still kept after 200 cycles at a high rate of 10 A g-1 with a low capacity loss of 0.08% per cycle.